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Re: xfs_growfs / planned resize / performance impact

To: Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>
Subject: Re: xfs_growfs / planned resize / performance impact
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sun, 5 Aug 2012 08:43:36 +1000
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
In-reply-to: <5017E426.2040709@xxxxxxxxxxxx>
References: <5017E426.2040709@xxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jul 31, 2012 at 03:56:54PM +0200, Stefan Priebe - Profihost AG wrote:
> Hello list,
> 
> i'm planning to create a couple of VMs with just 30GB of space while
> using xfs as the main filesystem.
> 
> Now i alreay know that some of the VMs will grow up to 250GB while
> resizing the block device and using xfs_growfs.

Just use thin provisioning and make it 250GB to begin with. Thin
provisioning mades filsystem grow/shrink pretty much redundant....

> Should i take care of that and format these disks with special parameters?
> 
> I've discovered that a 500GB volume has agcount=4 and 64000 blocks
> of internal log - while a 300GB volume resized to 500GB has agcount
> 7 ad only 40960 blocks of internal log.

I doubt you'll ever notice the difference.

> Is it a problem if this grow will happen in small portions (30GB =>
> 50GB => 75GB => 100GB => ... 300GB)?

Growing a filesystem by an order of magnitude is the limit of what
I'd suggest is sane. Growing it by two orders of magnitude
(espcially if you start with a 16 AG filesystem because of stripe
alignment) is going to cause problems with the number of AGs and
the subsequent freespace management scale issue....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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